Dissertations / Theses on the topic 'Icehouse'

Through the analysis of the stratigraphic and spatial distribution of organic walled dinoflagellate cysts (dinocysts) from climatologically and oceanographically key sites, this project aims to contribute to a better understanding of the Eocene-Oligocene (E/O) environmental changes and their timing. A central issue is to identify the global environmental changes which are responsible for the Eocene cooling and its underlying mechanisms with the focus on the Oligocene isotope-1 (Oi-1) event, thought to mark the onset of major Antarctic glaciation.

Two low-latitude sites were selected, Blake Nose (western North Atlantic) and Massignano (central Italy). For the first time a coherent taxonomy and biostratigraphy of dinocysts was established for the late Eocene at these latitudes. A high resolution correlation was established between the Massignano E/O Stratotype Section and the stratigraphically more extended ‘Massicore’. The composite section was used to analyse sea surface temperature (SST) change across the greenhouse-icehouse transition by means of dinocyst distribution.

At Massignano, the Oi-1 event was recognised both qualitatively and quantitatively. In the power spectrum of the SST_dino the ~100 and ~400 kyr eccentricity cycles may be distinguished and correlated with La04. When orbitally tuned, the E/O GSSP dates ~100 kyr older than the Oi-1 event. The boundary’s age could either be ~33.75 or ~34.1 Ma, both differ significantly from the ~33.9 Ma age in the GTS 2004.

Furthermore, when the data from the low-latitude sites were combined with extensive datasets from the Proto North Atlantic and adjacent regions, a suite of species sensitive to changes in SST was recognised. Their first and last occurrences reflect seven distinct phases of decreasing SSTs during the Middle Eocene to earliest Oligocene.

These results clearly indicate that atmospheric cooling together with higher frequency orbital forcing played a key role in the transition from the Greenhouse to the Icehouse world.

Tropical reefs, constructed during the late Palaeozoic icehouse climate, suffered high amplitude, high frequency sea level changes (Gondwanan glaciation). Rare three-dimensional outcrops of Virgilian (Pennsylvanian) and Wolfcampian (Early Permian) reefs occur in the Hueco Mountains, Texas. The reefs form part of a highly cyclical carbonate platform succession that suffered repeated emergence. The reefs are dominated by platy 'phylloid algae', these algae may belong to either Rhodophyta or Chlorophyta. The erect, recumbent or cyathiform genus Eugonophyllum is interpreted as belonging to the green algal family Halimedaceae. Eugonophyllum is the dominant reef building alga in the area studied. The prostrate phylloid alga Archaeolithophyllum is interpreted as belonging to the red algal family Corallinaceae. Archaeolithophyllum does not occur in the reefs, but forms extensive biostromes. The dominant constructional mechanism for reef formation has previously been regarded as sediment baffling and trapping, mainly by erect phylloid algae. Analysis of reef ecology clearly shows that these algae were in fact capable of forming a framework, to which considerable stability was added by secondary encrusting organisms such as the problematica Tubiphytes (or Shamovella) and Archaeolithoporella. Complex, multiple encrustations (both in-vivo and post-mortem) of these organisms were a fundamental element of reef construction. The effect of diagenesis on the phylloid algae and Tubiphytes are illustrated. Tubiphytes were found to be commonly altered on the ultrastructural scale, inferred to be by dissolution and reprecipitation, but with some preservation of microstructural features such as laminae.

Early diagenesis of icehouse carbonate is complex, but can significantly modify depositional porosity and permeability. During icehouse times, high-amplitude highfrequency sea-level oscillations cause subaerial exposure, with vertical migration of meteoric hydrological-zones (vadose, fireshwater and mixing-zone) through the platform sediments. Repeated cycles of subaerial exposure and associated meteoric diagnesis result in significant porosity inversion, as carbonate grains are dissolved and re-precipitated as calcite cement. This diagenetic overprinting generates a complex pattern of cementation and secondary porosity and permeability, the distribution of which cannot be predicted simple through study of diagenetic products.

Durante o Eoceno e o Oligoceno (55 a 23 Ma) a Terra esteve sujeita a período de grandes mudanças climáticas. Registros geológicos, reforçados por modelos climáticos, indicam que o clima global durante esse período passou de estágio praticamente livre de calotas polares para situacao climática próxima a que hoje podemos encontrar na Antártica. Grande parte desses registros são indiretos, retirados de sedimentos de fundo marinho ou de material fóssil. Evidência terrestre clara da variação climática (greenhouse-icehouse) para o Eoceno-Oligoceno pode ser encontrada em Wesele Cove, ilha Rei Jorge, Antártica Ocidental. Tais evidências correspondem a uma sucessão de cerca de 60m com pelo menos 13 derrames de lava basáltica, de alguns metros de espessura cada, sobreposta, em contato erosivo, por diamictito e arenito. A sucessão basáltica é correlacionada com a Formação Mazurek Point/Hennequin, datada radiometricamente como do Eoceno, e o diamictito e arenito correspondem ao Membro Krakowiak Glacier da Formação Polonez Cove, datada, paleontológica e radiométricamente como pertencente ao Oligoceno inferior. Cada camada de basalto toleítico exibe uma zona inferior, mais espessa (1 a poucos metros), de rocha fresca, que é seguida transicionalmente por uma zona de alteração, variando de alguns decímetros a 1-1,5 m de espessura. O pacote de basalto está inclinado 25º para leste, provavelmente por tectonismo. A sucessão foi recentemente exposta devido ao rápido recuo da atual geleira Wyspianski. A evidência inicial de campo sugere que a sucessão representa um registro geológico de variação paleoclimática de condições mais amenas para condições glaciais, que pode ser correlacionada com a mudança do ótimo climático do final do Eoceno (greenhouse) para as condições de icehouse do Oligoceno, registradas na curva de paleotemperatura cenozóica estabelecida pela determinação de 18O em carapaças de foraminíferos. Este estudo teve como foco central a análise estratigráfica e geoquímica da ocorrência, a fim de interpretar a sucessão de eventos paleoclimáticos documentados no afloramento e analisá-los, no contexto da história paleoclimática da Antártica. Os dados obtidos mostraram que a transição de zonas não alteradas para alteradas observada em cada derrame de basalto pode de fato ser atribuídas à ação moderada de processos intempéricos no topo de cada derrame. Eles também demonstram uma origem glacial, em parte subglacial com contribuição marinha, dos diamictitos sobrepostos, que apresentam feições, tais como, clastos de litologias e tamanhos variados, facetados e estriados, clastos tipo bullet shaped, clastos partidos por congelamento, estrias intraformacionais e fósseis marinhos encontrados na matriz do diamictito. As condições climáticas amenas responsáveis pelo intemperismo do basalto durou até o surgimento do último horizonte de lava, seguida por movimentação tectônica que inclinou o pacote. Esses eventos indicam condições paleoclimáticas menos rigorosas relativamente longas durante o Eoceno, precedendo o estabelecimento do manto de gelo oligocênico nesta parte da Antártica.
During the Eocene and Oligocene (55 23 Ma) the Earth was undergoing a period of great climatic changes. Geological records, reinforced by climate models indicate that global climate during this period went from a stage in which the Earth was virtually free of polar ice caps to a stage close to what we find today in Antarctica. Most of these records are indirect, taken from the deep-sea cores or fossil material. Clear terrestrial evidence of climate change (greenhouse-icehouse) for the Eocene-Oligocene transition is found in Wesele Cove, King George Island, West Antarctica. This evidence includes a succession of at least thirteen, few meters thick, basaltic lava flows overlain disconformably by diamictite and sandstone. The basaltic section is correlated with the Mazurek Point/Hennequin Formation, radiometric dated as Eocene, and the diamictite and sandstone correspond to the Krakowiak Glacier Member of the Polonez Cove Formation, dated as Early Oligocene, on paleontological and radiometric basis. Each tholeiitic basalt layer exhibits a lower, thicker (1 to few meters) fresh zone, transitionally followed up by a zone of saprolith, varying from decimeters to 1-1.5 m in thickness. The entire basalt package of around 60 m, is tilted 25º to the east. The succession has been recently exposed due to fast retreat of the present Wyspianski Glacier. The initial field evidence suggests that the succession represents the geological record of paleoclimatic variation from mild to glacial conditions, that could correlate with the change from the late Eocene optimum climatic (greenhouse) to icehouse conditions in the Oligocene, as recorded on the Cenozoic paleotemperature curve established by 18O determinations on calcareous foram tests. This study had focus on the stratigraphy and geochemistry analysis of the occurrence, in order to interpret the succession of palaeoclimatic events documented in outcrop and analyze them in the context of paleoclimatic history of Antarctica. Data obtained consistently showed that the supposed transition from unaltered to altered zones observed in each basalt layer may in fact be assigned to the moderated action of weathering processes on top of each flow. They also demonstrate a glacial, in partly subglacial with marine contribution, origin for the overlying diamictites, which has features such clasts of diverse lithologies and sizes, faceted and striated clasts, bullet shaped clasts, clasts broken by freezing and thaw, intraformational striae and marine fossils found in the matrix of the diamictite. The mild paleoclimatic conditions responsible for weathering of the basalt lasted until the emplacement of the highest lava horizon, followed by tectonic movement that tilted the package. These events indicate a relatively long paleoclimatic mild conditions during the Eocene, preceding the establishment and displacement of the Oligocene ice-sheet in this part of Antarctica.

To better understand how the evolution of Cenozoic deep-water circulation related to changes in global climate and ocean basin configuration, we generated Nd isotope records from Ocean Drilling Program sites in the southeastern Atlantic to track deep water mass composition through time. We used fossil fish debris from ODP Sites 1262-1264 (Leg 208), spanning present-day water depths of 2500-4750 m, to reconstruct the isotopic signature of deep waters over the past ~53 Ma. The data indicate an initial transition from relatively non-radiogenic values (??Nd=~-10) at 53 Ma to more radiogenic values (~-8.5) at ~32 Ma. From ~32 Ma to 3.85 Ma, the Nd signal becomes more nonradiogenic, ~-12.3 at the top of the record. Comparison of our data with Nd isotopic records derived from a North Atlantic Fe-Mn crust show similar non-radiogenic values (~-10.5) in the 53??32 Ma interval and a trend toward more non-radiogenic values beginning at ~20 Ma. The data likely reflect an overall shift from a Southern Ocean deep water source to the ultimate incursion of deep waters from the North Atlantic. The non-radiogenic values at the base of the record reflect a Southern Ocean source of deep water. The shift toward more radiogenic values indicates an increased contribution of Pacific waters to the Southern Ocean source as the tectonic gateways changed after ~35-33 Ma. The subsequent trend toward more non-radiogenic Nd isotope values is approximately concurrent with the increase of benthic foraminiferal ??18O values, based on comparison with a compilation of global data. Thus, changes in oceanic gateway configuration in addition to overall cooling and the build-up of continental ice on Antarctica may have altered the Nd isotope character of Southern Ocean deep waters during the early Oligocene.

Chemical weathering of silicate rocks removes carbon dioxide from the atmosphere at a rate roughly proportional to its atmospheric abundance. This negative feedback mechanism is widely believed to have kept the Earth's climate within habitable bounds since life emerged several billion years ago. However, the presence of continental ice sheets (an 'icehouse' world, such as at the present day) may weaken the feedback mechanism or even change its sign. In order to test this hypothesis, samples were collected from two soil chronosequences in Scotland and Wyoming and from lake sediments in California. The behaviour of several radiogenic (strontium (Sr) and neodymium (Nd) and stable (molybdenum (Mo), copper (Cu) and zinc (Zn) isotope systems during weathering were then investigated. The composition of Sr released from silicate minerals in soils deposited since the last deglaciation (~20 ka) was observed to change from relatively radiogenic to relatively unradiogenic compositions with increasing soil age. This finding can, in part, explain the observed glacial-interglacial variability in Sr isotope composition of runoff from the Sierra Nevada over the past 150 ka as recorded in lake sediments. Such glacial-interglacial variation in the continental Sr flux to the oceans would alleviate existing problems with the marine Sr budget according to previous modelling and would support the hypothesis that the nature of feedback between climate (and atmospheric CO2 levels) and weathering changes as the Earth moves between greenhouse and icehouse conditions. Mo, Cu and Zn isotopes were shown to be fractionated by various biogeochemical processes in soils from Glen Feshie and the Wind River Mountains, Wyoming. The heavy isotopic composition of dissolved riverine Mo and Zn was shown to be related to incongruent weathering processes, perhaps related to soil age, whereas Cu appeared to weather congruently. Fractionation by vegetation and the role of organic matter within soils was also shown to be important in controlling the isotopic composition, concentration and distribution of Mo, Cu and Zn.

This thesis addresses calcareous nannoplankton evolutionary and palaeoecological response across the Paleogene greenhouse to icehouse transition using newly drilled material from Sites U1408 and U1411 (IODP Expedition 342) in the North Atlantic. Calcareous nannoplankton were the dominant oceanic phytoplankton group in the early Paleogene yet declined in diversity and underwent significant assemblage restructuring through the middle Eocene to early Oligocene, coinciding with major climatic reorganisation. However the structure and timing of this nannoplankton response is poorly constrained due to few records of appropriate stratigraphic resolution. Here, exceptionally preserved calcareous nannofossils from stratigraphically expanded packages of Paleogene clay-rich drift sediments from IODP Expedition 342 are used to document diversity loss and population shifts in order to interpret the relationship between plankton evolution and palaeoclimatic and palaeoceanographic change in the North Atlantic across this key interval, with focus on abrupt climatic change at the Middle Eocene Climatic Optimum (MECO) and the Eocene-Oligocene transition (EOT). Results indicate low speciation rates combined with relatively high extinction rates drove calcareous nannoplankton diversity loss through this interval and palaeoecological analysis highlights three key intervals; middle Eocene stability, incorporating muted assemblage response to transient warming at the MECO, the late Eocene transitional phase and the EOT and early Oligocene population restructuring, with major assemblage shifts controlled by intensified surface water cooling and increased nutrient availability. Palaeoclimatic and palaeoceanographic changes through this transition led to reduced optimal habitat space for this phytoplankton group resulting in decline and extinction in many taxa and the proliferation of select opportunists at the onset of the icehouse world.

Un obstacle majeur à la caractérisation des paléoclimats en période de type « greenhouse » tient à la mauvaise préservation des archives sédimentaires et à des limites dans les calibrations des marqueurs géochimiques utilisés. Ces limitations entrainent de grandes incertitudes sur les valeurs et la répartition des températures des eaux de surface (SSTs) et des concentrations en CO2 atmosphérique. Les mécanismes qui ont fait basculer le système Terre d’un régime de type greenhouse à icehouse au cours du Paléogène restent donc encore mal contraints. Dans cette thèse, l’évolution thermique de l'océan superficiel et les pCO2 atmosphériques au cours du Paléogène ont étés estimées à partir du signal isotopique (δ18O et ∆13C) des exosquelettes carbonatés des coccolithophoridés : les coccolithes. Les données montrent un refroidissement global des SSTs de l’Eocène inférieur à moyen. A l’Eocène supérieur et au travers de la transition Eocène-Oligocène, les pCO2 diminuent et le refroidissement des hautes latitudes se poursuit, induisant la mise en glace de l’Antarctique, tandis que la ceinture tropicale se réchauffe. Ce bouleversement dans la répartition des flux de chaleur à la surface de la Terre est synchrone de la mise en place d’un courant circumpolaire antarctique plus vigoureux. Ces résultats mettent donc en évidence le rôle moteur des changements de circulations océaniques dans la dynamique climatique de cette transition. De plus, cette thèse prouve également l’existence de gradients thermiques latitudinaux importants tout au long du Paléogène. L'hypothèse d'une répartition homogène des SSTs entre l’équateur et les pôles, si difficile à modéliser peut être écartée
Among the major obstacles in constraining paleoclimates for periods of “greenhouse” type is the poor preservation state of the sedimentary archive, and the existence of limits for each of the different applied geochemical markers. These obstacles lead to great uncertainties on the values and distribution of sea surface temperatures (SSTs) and atmospheric CO2 concentrations. Therefore, the mechanisms that brought the Earth’s system from a “greenhouse” to an “icehouse” regime throughout the Paleogene are not well constrained. In this thesis, we reconstructed the thermal evolution of the superficial ocean and the evolution of atmospheric pCO2 during the Paleogene from the isotopic signal (δ18O and ∆13C) of the fossilized carbonate exoskeleton of coccolithophores: coccoliths. Our data reveal a global cooling of surface waters from the Early to the Middle Eocene. During the Late Eocene and across the Eocene-Oligocene transition, values for pCO2 decrease, and cooling at high latitudes continues, allowing for the set up of an ice sheet in Antarctic, while the tropical belt warms. This change in the distribution of heat fluxes at the Earth’s surface during this period is synchronous to the deepening of the Drake Passage and to the set up of a vigorous Antarctic Circumpolar Current. These results thus highlight the driving role of changing oceanic circulations for climate dynamics during this transition. This thesis also proves the existence of important latitudinal thermal gradients throughout the Paleogene. The hypothesis of a homogeneous distribution of SSTs between the Equator and the poles, which prevails in the literature but remains hard to modelise, can thus be rejected

The transition from the warm, “greenhouse” conditions of the Pliocene to the cold, “icehouse” conditions of the Pleistocene marks a significant development in climate history. The deep-ocean is the largest dynamic reservoir of heat and carbon dioxide in the climate system that is accessible on timescales of Plio-Pleistocene climate change. Therefore, changes in the state of the deep-ocean may have played an important role in large scale Plio-Pleistocene climate change via variability in the meridional overturning circulation of the Atlantic (AMOC). In this thesis, paleoceanographic reconstructions of Plio-Pleistocene Atlantic deep-water circulation are presented from the perspective of Ocean Drilling Program Sites 1264 (2505m depth) & 1267 (4350m depth), situated at ~30oS in the Southeast Atlantic. Reconstructions are based on high-resolution (~<5,000 year time-step), down-core measurements of oxygen (δ18O) and carbon (δ13C) stable isotope ratios in benthic foraminifera. During the Pliocene, widespread high δ13C values in the Atlantic and at Sites 1264 & 1267 indicate low nutrient conditions and active deep-water renewal. The early Pliocene closure of the Central American Seaway (CAS) (~4.7-4.2 Ma) is considered to have been influential in establishing strong deep-water formation in the North Atlantic. Evaluation of δ13O and δ13C records from Site 1264 and throughout the North Atlantic, however, indicate that the CAS closure event had only a limited impact outside of the Caribbean Basin. Meanwhile, during the interval ~3.6-2.7 Ma, δ13C-gradients between Sites 1264-1267 are near zero and suggest strong North Atlantic Deep Water (NADW) prevalence in the Southeast Atlantic, similar to or stronger than the modern situation. The transition into Pleistocene style glacial-interglacial cycles at ~2.7 Ma is associated with a reduction of NADW prevalence in the Atlantic, particularly during glacials and at depth. At ~2.4 Ma, δ18O and δ13C records from Sites 1264 & 1267 reveal marked changes in deep-water circulation. Large (>0.5‰) δ18O-gradients emerge, with heaviest values seen at Sites 1264 & 1267 compared to records from the North Atlantic. At the same time, δ13C values increase at Sites 1264 & 1267. The combination of high δ18O and δ13C values at Sites 1264 & 1267 is consistent with enhanced export of a dense component of NADW that enters the Atlantic from the Nordic Seas by spilling over the Iceland-Scotland Ridge. Comparisons with other North Atlantic records suggest that the pathway of Iceland-Scotland Overflow Water (ISOW) was restricted, flowing along the abyssal East Atlantic and piling up at Walvis Ridge. Between ~2.0-1.5 Ma, maximum δ13C values and minimum δ13Cgradients within the North Atlantic and between the North Atlantic and Sites 1264 & 1267 indicate that the overall export of NADW was strongest for the Pleistocene. After ~1.5 Ma, Atlantic δ18O-gradients begin to reduce, along with δ13C values, although δ13C-gradients still imply strong NADW export. Starting at ~1.3 Ma and across the Mid Pleistocene Transition (MPT), Atlantic δ18O-gradients reduced markedly, as did North Atlantic-Pacific δ18O-gradients but to a lesser degree. After ~0.9 Ma, glacial reductions in NADW presence at depth are the most severe of the entire Plio-Pleistocene, while interglacial export of NADW into the Atlantic remained almost as high as pre MPT conditions. Changes in the strength of AMOC during the Plio-Pleistocene are inferred through comparisons of Atlantic deep-water history with records of sea surface temperature from the high latitude North Atlantic, South Atlantic and North Pacific. I propose that AMOC played an important role in the evolution of Pleistocene climate. Enhanced northward heat transport, due to an increase in the strength of AMOC at ~2.4 Ma, limited the growth of continental ice sheets and sea ice within the North Atlantic region. This may have been caused by increased equator-to-pole thermal gradients and decreased atmospheric moisture transport, increasing salinity, as the global climate cooled. A strengthening of AMOC at ~2.4 Ma is paralleled by significant deep-water changes recorded at Sites 1264 & 1267, implicating enhanced ISOW export into the Southeast Atlantic as an important component of AMOC at this time. A maximum in AMOC occurred between ~2.0-1.5 Ma, along with warming in the mid latitude North Atlantic. Scavenged heat from the South Atlantic promoted enhanced cooling of the Southern Hemisphere and the expansion of sea ice at ~1.5 Ma. Feedbacks originating in the Southern Ocean then acted to cool the globe and eventually pre-condition the climate for the MPT.

The most recent transition, from a greenhouse to an icehouse climate state, occurred during the Eocene-Oligocene transition (~34 Ma) and is thought to have been driven by a long-term decline in carbon dioxide concentrations and/or changes in ocean heat redistribution as a result of tectonic gateway reorganisation. In order to determine the primary driving mechanisms responsible, this thesis reconstructs long-term terrestrial and marine temperature change during the Eocene (56.0-33.9 Ma) using an organic biomarker approach. During the descent towards the icehouse (48-34 Ma), high-latitudes (>55°) are characterised by gradual surface water cooling (~6.5 0c). During the same interval, low-latitude settings exhibit ~2.5 °C of cooling. An ensemble of fixed-C02 climate model simulations that span the Eoc'ene indicate that only a small percentage (~5 to 15%) of this reconstructed temperature change can be ascribed to ocean gateway reorganisation or paleogeographic change. As such, this indicates that atmospheric carbon dioxide was the most likely driver of surface water cooling during the middle and late Eocene (48-34 Ma). To explore this further, new terrestrial temperature records were obtained from marginal marine settings and terrestrial lignite deposits. During the early Eocene, terrestrial temperatures remain stable and warm and coincide with a long-term maximum in global surface water temperatures and atmospheric carbon dioxide. Insights from lignite deposits indicate that additional carbon cycle feedback mechanisms (e.g. methane cycling) may have also been important in regulating early Eocene warmth. During the middle and late Eocene, terrestrial temperatures remain stable or exhibit a gradual decline (~3 °C). The magnitude of terrestrial cooling is much smaller than observed in the marine realm and implies significant changes in ocean heat redistribution during the middle and late Eocene. Although changes in ocean heat redistribution are consistent with C02 drawdown, tectonic gateway reorganisation may have also been important in some regions.

The Upper Mississippian (Chesterian) Bluefield Formation of southeastern West Virginia and southwestern Virginia is the basal unit of the Mauch Chunk Group, a succession of predominantly siliciclastic strata sourced from actively rising tectonic highlands east of the Appalachian Basin. The Bluefield Formation conformably overlies shallow-marine carbonate units of the Greenbrier Group, and is unconformably overlain by incised fluvio-estuarine facies of the Stony Gap sandstone member (Hinton Formation). Outcrops along the Allegheny Front were investigated sedimentologically and structurally, and subjected to gamma ray analysis. Composite outcrop sections from deformed rocks of the Allegheny Front were correlated with the relatively undeformed rocks in the subsurface of the Appalachian Basin to the west using over 100 commercial oil and gas test wells. Regional subsurface cross-sections and isopachs define a depocenter in the southeastern part of the study area. Measured outcrop sections reveal that the stratigraphic record in the depocenter consists predominantly of meter-scale, upward-shallowing parasequences, each capped by a flooding surface. These parasequences are stacked into four regionally correlatable depositional sequences. On the basin margin to the southwest and northwest, incised valleys, and fewer meter-scale parasequences characterize depositional sequences. Stacking of parasequences into sequences reflects a hierarchy of greenhouse-type 5th order, and icehouse-type 4th order eustatic changes superimposed on differential subsidence. Due to early Alleghenian thrust loading, the depocenter experienced greater total accommodation, which prevented incision during lowstands. Instead, in the depocenter, lowstands are typified by preservation of 5th order coal-bearing parasequences. Basin-margin areas experienced less total accommodation resulting in development of 4th order lowstand incised valleys and erosive removal of parasequences. This study demonstrates that both tectonic and eustatic forcing mechanisms controlled stratigraphic evolution of the Bluefield Formation.
Master of Science

A study of 12 cores and 2 wells with cuttings through the Silurian (444 to 416 m..y.) succession of the Wabash Platform, Indiana was done to establish the high resolution sequence stratigraphy of a sediment-starved low-latitude epeiric sea platform during the transition from Ordovician icehouse to Devonian greenhouse. The Wabash Platform (approximately 200,000 square km area) is bounded to the north by the Michigan Basin, to the east by the Appalachian Basin, and passed to the southwest into the Vincennes Basin, which was open to the ocean. Facies developed include: crinoidal grainstone-packstone sheets (updip shoals), buildup facies (stromatactis wackestone - lime mudstone, below storm wave-base settings; stromatoporoid skeletal wackestone - floatstone, storm wave-base to fair-weather wave-base; and crinoidal rudstone to packstone; flank facies); non-cherty, skeletal packstone, wackestone, mudstone (sub-fair-weather- to storm wave-base); and cherty, skeletal wackestone - mudstone and variably argillaceous carbonate mudstone (below storm wave-base). Eight thin sequences (1.3 to 4 m.y. duration) occur and range from 2 m to 10 m, with the upper two sequences up to 20 m downdip; most of the sequences can be correlated to global cycles. Except for the lower three disconformity-bounded sequences, most sequences are relatively conformable and lack well defined sequence boundaries or subaerial exposure surfaces. The most easily mapped surfaces are the transgressive surfaces, given that the correlative conformities are cryptic. Lowstand system tracts probably include downdip grainy facies and the deep ramp seaward of updip late highstand deposits. Transgressive systems tracts are upward deepening, upward fining carbonate units, some of which become more argillaceous and silty upward. This contrasts with the usual association of clastic-prone units with lowstand to early transgressive systems tracts. Highstand systems tracts are subtly upward coarsening from carbonate mudstone to skeletal wackestone/packstone and rarely skeletal grainstone. During deposition of the uppermost two sequences, mudmound barrier banks grew upward into shallow water buildups to form a discontinuous raised rim (40 m relief) to the ramp. Even though subsidence rates were very low (<1 cm/k.y.), the low sedimentation rates (0.3 cm/k.y. to 0.8 cm/k.y.) generally prevented the seafloor from building to sea level except for the basal three sequences in which Early Silurian third order glacio-eustacy generated disconformable boundaries. Thus the ramp remained subtidal through most of the relatively ice-free greenhouse later Silurian except over the buildups which locally shallowed to sea level. Parasequence development in high accommodation settings elsewhere in North America are compatible with the transition from moderate ice-sheets to an ice free world. However, this is poorly expressed on the Wabash Platform due to the dominantly deeper subtidal setting. The Silurian provides a window into climate change from a global cool period to global hothouse, which may have implications for understanding future climate change.
Master of Science

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The controls on organic carbon preservation in sediments are poorly understood, however there is a first order association between high total organic carbon concentration (TOC), warm climates and fine grained sediments with mature mineralogy in the geologic record. Permo-Carboniferous marine sediments in the Arckaringa Basin, however, present an exception with anomalous organic carbon concentration (<11% TOC) occurring within mineralogically immature siltstones deposited in deep, narrow (marine) fjords during glacial conditions. Organic matter (OM) is not refractory terrigenous material, but rather hydrogen-rich and labile, thus identifying an active preservational mechanism that differs from conventional organic carbon enrichment controlled by mineral preservation effects. Energy Dispersive Spectrometry (EDS) reveal an association between labile OM and high sulphur concentrations, and EDS mineral mapping identifies a cyclic millimetre alteration between sulphur/OM rich laminae and manganese carbonate (kutnohorite) laminae, identifying oscillating benthic redox conditions similar to annual varves in proglacial environments. Framboidal pyrite (<5 µm) is abundant only within organic-rich laminae, indicating sulphate reduction in euxinic conditions resulting from restricted sea water exchange and the development of strong density stratification. Seisimic profiles indicate that deposition occurred in fjord-shaped troughs, with restriction resulting from end moraines acting as sills to the open ocean. Thus, organic carbon enrichment is attributed to restriction in the ancient fjords, leading to periods of hydrogen sulphide build up within the water column that were annually flushed with seasonal change in temperature and runoff. The reducing conditions of the fjord provided a chemical trap for S leading to its enrichment in organic matter. Similarly, Mn within carbonates was enriched in the same manner. Excess dissolved sulphur build up in the water column and sediments resulted in vulcanization (sulfurization) reactions polymerizing labile organic compounds (lipids and carbohydrates) and their preservation as organosulphur compounds during early diagenesis.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2014

The Pennsylvanian Marble Falls Formation in the Llano Uplift region of the southern Fort Worth Basin (Central Texas) is a Morrowan-Atokan mixed carbonate-siliciclastic unit whose deposition was influenced by icehouse glacioeustatic sea-level fluctuations and foreland basin tectonics. Previous interpretations of the Marble Falls Formation focused on outcrop data at the fringes of the Llano Uplift. This study uses a series of 21 cores to create a facies architectural model, depositional environmental interpretation, and regional sequence stratigraphic framework. On the basis of core data, the study area is interpreted to have been deposited in a ramp setting with a shallower water upper ramp area to the south and a deeper water basin setting to the north. Analysis of cores and thin sections identified 14 inner ramp to basin facies. Dominant facies are: (1) burrowed sponge spicule packstone, (2) algal grain-dominated packstone to grainstone, (3) skeletal foraminiferal wackestone, and (4) argillaceous mudstone to clay shale. Facies stacking patterns were correlated and combined with chemostratigraphic data to improve interpretations of the unit’s depositional history and form an integrated regional model. The Marble Falls section was deposited during Pennsylvanian icehouse times in a part of the Fort Worth Basin with active horst and graben structures developing in response to the Ouachita Orogeny. The resulting depositional cycles reflect high-frequency sea-level fluctuations and are divided into 3 sequences. Sequence 1 represents aggradational ramp deposition truncated by a major glacioeustatic sea-level fall near the Morrowan-Atokan boundary (SB1). This fall shifted accommodation basinward and previously distal areas were sites of carbonate HST in Sequence 2 deposition following a short TST phase. Sequence 3 represents the final phase of carbonate accumulation that was diachronously drowned by Smithwick siliciclastics enhanced by horst and graben faulting. These findings contribute to our understanding of the depositional response to glacioeustatic sea-level changes during the Pennsylvanian and can also form the basis for constructing a sedimentological and facies analog for Morrowan to Atokan shallow- to deepwater carbonates in the Permian Basin and the northern Fort Worth Basin.
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Global climate is controlled by two factors, the amount of heat energy received from the sun (solar insolation) and the way that heat is distributed Earth's surface. Solar insolation varies on timescales of 10s to 100s of thousands of years due to changes in the path of Earth's orbit about the sun (Milankovitch cycles). Earth's internal boundary conditions, such as paleogeography, the presence/absence of polar icecaps, atmospheric/oceanic chemistry and sea level, provide distribution and feedback mechanisms for the incoming heat. Variations in these internal boundary conditions may happen abruptly or, as in the case of plate tectonics, take millions of years. We use geochemical and sedimentological techniques to investigate the response of ocean chemistry, regional aridity and atmospheric and oceanic circulation patterns to climate change during both greenhouse and icehouse climates. To explore the connection between orbitally-forced changes in solar insolation, continental aridity and wind, we generated a high-resolution dust record for ~58 Myr old deep-sea sediments from Shatsky Rise. Our data provide the first evidence of a correlation between dust flux to the deep sea and orbital cycles during the Early Paleogene, indicating dust supply (regional aridity) responded to orbital forcing during the last major interval of greenhouse climate. The change in dust flux was comparable to that during icehouse climates implying subtle variations in solar insolation have a similar impact on climate during intervals of over-all warmth as they do during glacial-interglacial states. The Carboniferous Period (359-299 Ma) marks a critical time in Earth's history when a series of tectonic and biological events caused a shift in the mean climate state from a global "greenhouse" to an "icehouse". Geochemical records extracted from sedimentary rocks deposited in shallow epicontinental seaways are increasingly being used to infer relationships between tectonism, carbon cycling and climate and therefore are assumed to reflect global ocean processes. We analyzed radiogenic isotopes in biogenic apatite along a North American transect to constrain the degree of geochemical coupling between the epicontinental seas and the open ocean. Our results argue strongly for decoupling of North American seaways from the open ocean by latest Mississippian time.